Irma's final phase: Flooding in the Southeast is biggest concern

(This article, first posted at 11:15 p.m., was updated at 5:15 p.m. to reflect the latest National Hurricane Center advisory and current conditions in the Southeast)

Irma weakened to a tropical storm Monday morning and is expected to further weaken by Tuesday to a tropical depression. But this storm, while wounded, is still dangerous. Both storm surge and inland flooding, which cause the majority of deaths in tropical cyclones, remain a risk over the Southeast states.

Charleston, S.C. was also under a flash flood emergency through 8:15 p.m.. "The combination of extremely high tides combined with heavy rain has resulted in widespread, dangerous flooding throughout Downtown Charleston," the National Weather Service said.

Due to heavy rain and areas of flooding throughout South Carolina, the state's emergency management division tweeted: "Dangerous conditions throughout much of South Carolina. Remain where you are if you're safely able to do so."

At 5 p.m., the storm center was plowing north-northwest through southern Georgia at 17 mph, about 150 miles south of Atlanta. Peak sustained winds had dropped to 50 mph, but higher gusts were reported.

(National Hurricane Center)

Due to the storm's enormous size, tropical-storm-force winds, capable of downing trees and causing outages, extended a lengthy 415 miles from the center. Atlanta's Hartsfield-Jackson International Airport clocked a gust to 64 mph Monday afternoon.

Water levels will continue to be elevated above normally dry land along a section of Florida's Gulf Coast and in coastal Georgia and southern South Carolina. A storm surge warning extended over these areas, and the National Hurricane Center warned Monday that "life-threatening" coastal inundation remained possible.

In areas where peak surge coincided with high tide, water levels were predicted to rise as much as 6 feet above normally dry land from the Georgia to central South Carolina coast on the storm's Atlantic side, and from near Clearwater, Fla. to the state's Big Bend area on the Gulf of Mexico side.

These are the hurricane center's forecasts for the maximum water level at different locations if the surge peaks at high tide:

Surge flooding also occurred in Charleston, S.C., on Monday, reaching its worst around high tide midday Monday. "Avoid Downtown Charleston, roads already closing across the city," the Weather Service tweeted.

Rainfall forecast through Thursday from the National Weather Service. (WeatherBell.com)

Rain covered central and northern Georgia late Monday afternoon, as well as all of South Carolina, and almost all of Alabama. In many areas, the rain was falling heavily.

"Intense rainfall rates are leading to flash flooding and rapid rises on creeks, streams, and rivers," the National Hurricane Center said.

The heaviest rainfall is expected to focus over northern Georgia, South Carolina and northern and eastern Alabama through Monday night.

"Significant river flooding will persist over the Florida peninsula in the wake of Irma and in Georgia, South Carolina and north-central Alabama, where additional heavy rains are expected," the Hurricane Center said. "Portions of these states within the southern Appalachians will be especially vulnerable to flash flooding."

Into Tuesday, the heaviest rain will spread north and west into the western Carolinas and Tennessee, and northern Mississippi. In these areas, the NWS predicted 2 to 4 inches of rain and locally higher amounts. The service also cautioned that local flooding could occur.

Through late Monday afternoon, widespread rainfall totals of 6 to 10 inches were reported over the Florida peninsula into southeast Georgia, with pockets of 10- to 15-inch totals.

Irma made two landfalls Sunday: Over the Florida Keys and on Marco Island, Fla. Wind gusts to at least 90 mph were widespread over the peninsula, occurring far away from the storm's center, due to its size.

Here are some of the peak wind gusts that have been logged by the National Weather Service:

Jason SamenowJason Samenow is The Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association. Follow